Traditionally, as thermal-type fluid flow sensor used in the air flow meter for measuring the quantity of intake air fitted in the electronically controlled fuel injection device of an internal engine of an automobile and the like, thermal-type products have constituted the main stream because they can detect directly the mass quantity of air. Among them, the thermal-type air flow sensor produced by the semiconductor micromachining technology has attracted attention in particular because it can reduce cost and be driven with a low power.
As the prior art for such air flow sensor, for example, JP-A No. 8 (1996)-54269 proposes one in which a heater and two sensors sandwiching this heater are disposed in the center of the sensor. In order to secure the precision of measurement of this air flow sensor, the consistence at all times of the environment of sensors is a premise. Therefore, it is necessary to control temperature so that there may be a predetermined difference of temperature between the heater temperature and the temperature of air that flows in.
And JP-A No. 10 (1998)-311750 proposes one in which an intake air sensor for measuring air that flows in addition to the heater and temperature sensor are disposed. For example, if the predetermined temperature difference is set at 100° C., a feedback control is made so that the heater temperature may be 120° C. against an intake temperature of 20° C. For this purpose, the direct heater resistance value has been used in the product having the configuration. However, the elements deteriorated due to the heating of the heater itself, and the resulting change in the resistance value made it difficult to maintain precision.
As a means of solving this problem, JP-A No. 2002-277483 proposes the disposition of a heater temperature sensor for measuring the heater temperature beside the heater so that the heater temperature may always be maintained without being subjected to the impact of any heater deterioration.